Grinding machine

ABSTRACT

THE INVENTION RELATES TO A GRINDING MCHINE AND, MORE PARTICULARLY, TO APPARTUS FOR FINISHING SURFACES OF REVOLUTION BY THE ABRASIVE PROESS, WHEREIN THE FORCES BETWEEN THE ABRASIVE WHEEL AND THE WORKPIECE ARE MAINTAINED AT ACCURATELY-DETERMINED LEVELS.

Nov. 9, 1971 E G. ROBlLLARn ErAL 3,618,269

GRINDING MACHINE Filed Aug. 1. 1969 2 Sheets-Sheet 1 HERBERT R. UHTENWOLDT PAUL A. LEPPANEN INVENTORS.

Nov. 9 1,971 E; G, RomLLARn ErAL 3,618,29

GRINDING MACHINE Filed Aug. 1,v 1969 2 sheets-sheet United States Patent O1 hee 3,618,269 Patented Nov. 9, 1971 3,618,269 GRINDING MACHINE Edward G. Robillard, Cherry Valley, Herbert R. Uhten- Woldt, Worcester, and Paul A. Leppanen, Gardner,

Mass., assignors to The Heald Machine Company,

Worcester, Mass.

Filed Aug. 1, 1969, Ser. No. 846,901 Int. Cl. B24b 49/08 U.S. Cl. 51-165.9 5 Claims ABSTRACT F THE DISCLOSURE This invention relates to a grinding machine and, more particularly, to apparatus for nishing surfaces of revolution by the abrasive process, wherein the forces between the abrasive wheel and the workpiece are maintained at accurately-determined levels.

BACKGROUND OF THE INVENTION It is well known in the grinding art that the use of so-called controlled force feed provides many advantages in such operations. This type of feed takes place when grinding is carried out by control of the force between the abrasive wheel and the workpiece surface to be iinished, while the rate of feed varies. This method is contrasted with the feed rate method in which the rate is controlled and the force varies. Controlled force grinding, among other things, provides for more rapid grinding, since the force can be selected at the point just below the force where the wheel deteriorates. Since the removal of metal is proportional to the force between the 'wheel and the workpiece, the optimum speed of grinding is accomplished. This is important when it is to be considered that the machine represents a large capital investment which should be used at its optimum effectiveness. Controlled force grinding also provides the advantage that the surface quality can be held at a desired value, neither more nor less than is desired for the workpiece; the amount of force between the wheel and the workpiece, of course, determines to a great extent wha-t the nish shall be. During the grinding cycle, therefore, under proper conditions, the force should be adjusted to take care of the particular portion of the cycle with which one is concerned. For instance, during the roughing grind, the important thing is to remove metal as fast as possible and high forces are used. At the end of the finish cycle, particularly, one should use a low value of force to give a smooth, fine nish and also to give better control over size and geometry at that point. In the past, however, close control of the forces has been a very very dicult matter and the methods used have not been entirely successful. For instance, it has been suggested that the force be measured at all times by use of a transducer located on the wheel spindle, since the Wheel spindle deflection or deformation is directly proportional to the force between the wheel and the workpiece. Not only does this involve very expensive apparatus, but the gages which do the measuring must be placed in a very awkward place on the surface of the spindle where they not only interfere with grinding, but are subjected to the dirt and moisture present in the grinding part of the machine. These and other difliculties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a grinding machine in which the force between the wheel and the workpiece is measured and controlled during certain critical portions of a grinding cycle.

Another object of this invention is the provision of a grinding machine using the controlled-force principle,

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wherein the optimum force is used at the various portions of the cycle.

A further object of the present invention is the provision of a grinding machine having a simple and inexpensive means for continuously measuring working force.

Another object of the invention is the provision of a grinding machine having a force-regulating mechanism located in a protected part of the machine.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

SUMMARY OF THE INVENTION In general, the invention consists of a grinding machine having a base with a table slidably mounted on the base and an actuator producing a force to bring about movement of the table relative to the base. A deformable member is interposed on occasion between the table and the base to transmit at least a portion of the actuator force between the two, and a strain gage is mounted on the dedormable member to indicate at all times the level of the force thus transmitted.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings, in which:

FIG. l is a plan view of a grinding machine embodying the principles of the present invention,

FIG. 2 is a vertical sectional View of the machine taken on the line II-II of FIG. l,

FIG. 3 is an enlarged sectional View of a portion of the apparatus shown in FIG. 2,

FIG. 4 is an elevational view of a modified form of the invention, and

FIG. 5 is a sectional view taken on the line V-V of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring rst to FIG. 1, wherein are best shown the general features of the invention, the grinding machine, indicated generally by the reference numeral 10, is shown as consisting of a base 11 having a at horizontal upper surface on which are mounted a workhead 12 and a wheelhead 13. The workhead is carried on a workhead table 14 which is mounted for longitudinal motion on the base 11 by means of ways 15'. Similarly, the wheelhead 13 is carried on a wheelhead table 16 which is mounted for transverse sliding motion on the base 11 by means of ways 17. Extending between the wheelhead table 16 and the base 11 is a feed cylinder 18 which is suitably provided with uid pressure through a conduit leading from a pressure regulating valve to bring about movement of the table 16 transversely of the base. Similarly, a hydraulic cylinder 19 connects the table 14 to the base 11 and brings about longitudinal movement of the table 14 over the ways 15.

Extending from the wheelhead 13 is a rotatable spindle 21 carrying on its outer end an abrasive wheel 22. Carried by the workhead 1:2 and rotated thereby is a workpiece 23; for the purpose of illustration, this workpiece is shown as the race of a ball bearing. The inner bore is being ground by the abrasive wheel 22 and the workpiece is supported on its outer cylindrical surface. Residing in the bore of the workpiece during the grinding operation is a pneumatic air gage 24 of the well-known type, which gage is connected to a control box 25. The control box 215 provides a ow of air to the gage 24 in a well-known manner. The amount of air that is able to pass between the surface of the gage and the surface of the bore of the workpiece is an indication of the workpiece size, and this flow is transmitted to the control box which contains various pressure switches to operate electrically to open and close solenoid valves in the hydraulic circuitry of the machine.

Slidable on the upper surface of the base 11 is a block 26 which, at its rearward end, is threadedly attached to a threaded shaft :27 which, in turn, is driven by a motor 28 fastened to the base 11i. This motor is of the type capable of small discrete rotary increments in response to pulses received from an electrical control. By regulating the nature and number of the pulses from the electrical control, it is possible to rotate the motor quickly or slowly in exact amounts to make the block 26 move transversely over the surface of the base 11. In the present apparatus, this motor is used to produce compensation after dress and to provide for retraction ofthe wheel at a suitable time in the grinding cycle, as is well known. A dressing diamond 29 is mounted on the workhead table 14' in position to engage the wheel 22 during a dressing traverse at a suitable time in the grinding cycle.

The block 26 is provided with a transverse slot 31 and in this slot resides a horn 32' extending downwardly from the undersurface of the wheelhead table 16. The front of the block 26 is provided with a hardened metal insert 33. Mounted on the front portion of the wheelhead table 16 is a retractable stop 34 having a contact rod 35 extending toward the block 26 and toward the metal insert 33. Mounted at the front of the retractable stop is a gear 36 and to the right (in FIG. 12) is an adjusting knob 37.

Referring now to FIG. 2, it can be seen that the gear 36 is attached to the outboard end of the rod 35 and that the gear is contacted by a feed-back `mechanism 38. This feed-back mechanism consists of a housing '39 having a bore 41 in one end of which is slidably carried a piston (not shown). It can be seen that the feed-back mechanism 38 is mounted on the underside of the housing of the retractable stop 34 by means of a bracket 63.

The forward end of the slot 31 in the block 26 is provided with a hardened metal button 61 adapted to engage, on occasion, a similar hardened metal button 62 located on the forward surface of the horn 32.

In FIG. 2, it can also be seen that the contact rod is made up of a central shaft 64 mounted in a sleeve 65 and locked against rotation relative thereto. At its outboard end, the sleeve is provided with a threaded portion 66 which threadedly engages the interior threaded 'oore of a nut 67. The exterior of the nut 67 is also threaded and is threadedly engaged in the interior of a threaded bore in the housing. The nut 67 is also bolted to the ratchet wheel or gear 36. The sleeve 65 is surrounded by a larger sleeve 68 located inwardly of the threaded portion 66. Between the inner surface of the sleeve 68 and the outer surface of the sleeve 65 are located a number of small bearing balls 69. Furthermore, pressure oil is provided in this same space through a passage 711 extending through the sleeve 68. This hydraulic pressure operates to bias the sleeve 65 rearwardly at all times and acts as a piston to take up all backlash between the threaded engagements with the nut 67.

Extending into the arm 59 of the table 16 is a conduit 42 leading to a horizontal bore 43 extending to a rear surface of the arm 59. `In the bore lies a piston 44 having a groove in its central portion leading to a drain passage 45. The outer end of the piston 44 is provided with a protuberance 46 which engages a deformable member- 47 which, in turn, on occasion, engages an insert 33 on a forwardly-facing surface of the block 26.

FIG. 3 shows the details of the deformable member 47 and associated elements. The deformable member 47 has a first lower portion 48 which is fastened to the arm 59. It is also provided with an upper second portion 49l which is generally in alignment with the protuberance 46 on the piston 44 and with the element 33 mounted on the slide 26. The second portion 49 is provided with a metal ball 55 with which the protuberance 46 actually makes engagement. The deformable member is provided with a relatively thin web 72 which is integral with and joins the first portion 48 to the second portion 49. Mounted on the side of the web 72 facing toward the horn 32 is a strain 'gage 73 of the well-known SR-4 type. This is a type of strain gage which, when stressed, changes its electrical resistance appreciably; this change of electrical resistance constitutes an indication of the degree of stress. The strain gage is connected by wires 74 which are connected at the other end to a connector member 75 from which are connected through a cable 76 to a control box 77. Electrical leads 78 are connected at opposite sides of a servo valve 79.

FIGS. 4 and 5 show a modified Version of the deformable member and the linear actuator. The deformable member 81 consists of an annular `iirst outer portion 82 which is bolted to a main body 83. It also is provided with a second inner portion `84, the right-hand part of which is cylindrical and resides in a bore formed in the housing 83. Extending between the rst portion 82 and the second portion 84 is a thin-walled diaphragm 86. The center of the second portion `84 is provided with a button 87 for contact with the button 54 of the block 26. The bore 85 is connected to pressure oil by a passage 88, while it is connected to drain by a passage `89. Fastened to the diaphragm 86 is a strain gage 91 which is located so as to be partly on the diaphragm 86 and partly on the inner second portion 84. A second strain gage 92 is located so as to be partly on the diaphragm 86 and partly on the outer first portion 82. Suitable sealing, such as an O-ring 93, is interposed between the main body 83 and the first or outer portion 82 of the deformable member. By this arrangement, there is formed an annular chamber 94 between the diaphragm 86 and the housing 83 which is used for drain from the hydraulic actuator formed by the second portion 84 and the bore 85. The bottom part of this chamber is connected to the drain passage 89.

The operation of the apparatus will now be readily understood, in view of the above description. The grinding cycle takes place in the usual Way by the feeding of the tables 14 and 16 relative to one another carrying the abrasive wheel 22 into the workpiece 23 for a grinding operation. The cross-feed takes place by means of the cylinder 18 under the controlled-force principle, since, in accordance with well-known constructions, the cylinder is provided with oil under a regulated predetermined pressure. Rough grind usually takes place in accordance with a high force and, at the end of this part of the cycle, the abrasive wheel 22 is carried out and dressed by the diamonds 29. When the abrasive wheel is returned to the workpiece for the `linish grinding operation, a lower oil pressure will be used in the cylinder `18 to provide a low force finishing operation. Toward the end of the linishing operation, as the gage 24 indicates to the control 25 that the final size is close to being reached, the table 16 continues to move to the rear of the machine (or to the left in FIG. 2), so that, first of all, the rod 35 engages the insert 33 on the block. Continued rearward movement of the table 16 produces a pressure of the rod 35 against the block 26, and the table is permitted to move rearwardly only by the retraction of the rod. At the same time, the deformable member 47 is making contact with the element 33 at the front of the slide block 26, which block is located on the base 11 of the machine and is firmly but adjustably connected thereto. As the table continues to progress rearwardly and grinding continues to take place, the deformable member 47 is bent, particularly in the area of the web 72, and this makes itself indicated in the strain gage 73, which indication is carried out to the control box 77 and the information is acted upon; for instance, by terminating the grinding operation entirely when deformation takes place to a predetermined extent.

One of the interesting features of the present construction is that the total force originating in the cylinder 18 is divided into three parts and the proportion of the division changes as the table 16 moves rearwardly. Part of the force exists in the grinding force between the wheel 22 and the workpiece 23 and results in deformation of the spindle 21. Part of the force is absorbed in the contact between the rod 3S and the insert 33; while the third part is absorbed by the contact between the element 33 and the deformable member 47. As the member 47 is increasingly deformed, this subtracts from the force available between the Wheel and workpiece as the cycle progresses.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come Within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. A grinding machine, comprising (a) a base,

(b) a table slidably mounted on the base,

(c) an actuator directly connecting the base to the table producing a force to bring about movement of the table relative to the base,

(d) a deformable member interposed on occasion between the table and the base independently of the actuator to transmit at least a portion of the actuator force between the table and the base,

(e) a linear actuator mounted to bring a selected force to bear on the deformable member to give it a prestress, and

(f) a strain gage mounted on the deformable member 6 to give a continuous indication of the force thus transmitted between the table and the base.

2. A grinding machine as recited in claim 1, wherein a first portion of the deformable member is attached to the table and second portion spaced from the first portion is contacted on occasion by a button associated with the base.

3. A grinding machine as recited in claim 2, wherein the linear actuator is mounted in the table to operate in alignment with the said second portion of the deformable member and the button.

`4. A grinding machine as recited in claim 3, wherein the linear actuator is a piston slidable under hydraulic pressure in a bore and the two portions of the deformable member are joined by a web of relatively small cross-section on which the strain gage is mounted.

S. A grinding machine as recited in claim 3, wherein the dirst portion is an annulus and the second portion is a piston slidable in a bore under the influence of hydraulic pressure, and wherein an integral diaphragm extends radially from the rst portion to the second portion and carries the strain gage.

References Cited UNITED STATES PATENTS 2,834,160 5/1958 Lillie 51-165 3,209,498 10/1965 Dall 51-165 3,274,738' 9/ 1966 Kuniholm 51-165 3,417,512 12./1968. Robillard et al 51-165 LESTER M. SWINGLE, Primary Examiner 

